Differential Diagnosis for 0.5cm Diameter Round, Smooth-Edged Opacity on Chest X-ray After a Car Accident

• Single Most Likely Diagnosis
  • Pulmonary contusion: This is a common injury after a car accident, where the lung tissue is bruised, leading to bleeding and edema, which can appear as a round opacity on a chest X-ray.
• Other Likely Diagnoses
  • Hemothorax: Blood in the pleural space can cause a round or oval opacity on a chest X-ray, especially if it is located and not freely flowing.
  • Pulmonary laceration: A tear in the lung tissue can fill with blood or air, appearing as a round opacity.
  • Pneumonia: While less directly related to trauma, pneumonia can cause round opacities, especially if the patient has been hospitalized or has a compromised immune system.
• Do Not Miss Diagnoses
  • Pulmonary embolism: Although typically presenting with more diffuse or wedge-shaped opacities, a pulmonary embolism can sometimes appear as a round opacity, especially if it is small. Given its high mortality rate, it's crucial not to miss this diagnosis.
  • Aortic dissection or rupture: While not directly causing a pulmonary opacity, an aortic dissection can lead to a mediastinal hematoma, which might be visible on a chest X-ray and could indirectly suggest the presence of an aortic injury.
• Rare Diagnoses
  • Pulmonary arteriovenous malformation (AVM): These are abnormal connections between arteries and veins in the lungs, which can appear as round, well-defined opacities on a chest X-ray. They are rare and usually congenital.
  • Hamartoma: A benign lung tumor that can appear as a round, smooth-edged opacity on a chest X-ray. Hamartomas are rare and typically asymptomatic.
  • Metastasis: If the patient has a known primary malignancy, a solitary pulmonary metastasis could appear as a round opacity. However, this would be less likely in the acute setting of a car accident unless the patient has a known cancer history.